Open Journal of Geology, 2016, 6, 158-164 Published Online March 2016 in SciRes. http://www.scirp.org/journal/ojg http://dx.doi.org/10.4236/ojg.2016.63015

How to cite this paper: Kotsarenko, A., Yutsis, V., Grimalsky, V. and Koshevaya, S. (2016) Detailed Study of Radon Spatial Anomaly in Tlamacas Mountain Area, Volcano Popocatepetl, Mexico. Open Journal of Geology, 6, 158-164. http://dx.doi.org/10.4236/ojg.2016.63015

Detailed Study of Radon Spatial Anomaly in Tlamacas Mountain Area, Volcano Popocatepetl, Mexico Anatolyi Kotsarenko1*, Vsevolod Yutsis2, Vladimir Grimalsky3, Svetlana Koshevaya3 1Facultad de Ingeniería, Universidad Autónoma del Carmen, Cd. del Carmen, México 2División de Geociencias Aplicadas, Instituto Potosino de Investigación Científica y Tecnológica, San Luis Potosí,

Mexico 3Centro de Investigación en Ingeniería y Ciencias Aplicadas, Universidad Autónoma del Estado de Morelos, Cuernavaca, México

Received 13 February 2016; accepted 14 March 2016; published 17 March 2016

Copyright © 2016 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/

Abstract Results of a soil radon survey accomplished by 2 different methods during 2 different periods in the area of Tlamacas Mountain are presented. The first study, carried out from 15-APR-2010 to 09-MAY-2010 in 30 measurement sites by means of CR39 solid state nuclear detectors, shows 2 active zones with intensive radon emanation with a characteristic dimension of about 300 meters located in the northwestern and western parts of the Mountain. The second survey, made on 05-JUL-2011 in 23 measurement sites with 10 min sampling by a SARAD RTM 1688 Radon/Thoron monitor, in contrast, revealed a sizeable area depleted in radon and 3 active areas of increased radon release in the lateral Mountain sides. These observed phenomena strengthen our assump-tion about the presence of an active geological structure in Tlamacas Mountain connected with a geodynamical processes in volcano Popocatepetl.

Keywords Radon, Tlamacas, Mexico, Anomaly, Popocatepetl, Monitoring

1. Introduction Our earlier studies in the volcano Popocatepetl area (Figure 1, Lat. 19.07˚N, Long. 98.63˚W, elevation 5465 m)

*Corresponding author.

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Figure 1. Volcano Popocatepetl, topographic map [2].

have shown the variety of anomalies in Radon behavior associated with volcanic activity [1]. Monitoring of soil radon release in 3 different volcanic sites has shown several cases of decreasing radon concentration during times of approaching moderate volcanic eruptions. A soil radon survey and gamma ray spectrometry revealed intensive radon and gamma ray emanation located in the area of Tlamacas Mountain; the radon concentrations in the Tlamacas area were 10 - 20 times greater than the background volcano values. A new conception of the coupling between the lithosphere and the atmosphere was also presented: intensive radon release modifies the electric circuit between the ground and thunderclouds, provoking micro-discharges in the air and attracting light- nings.

In order to interpret results on the correlation between radon behavior at Tlamacas station with moderate eruptions of volcano Popocatepetl, more studies in the Tlamacas area were desirable. Additionally, different questions in relation to the radon anomaly in Tlamacas Mountain (Figure 2), [1] have arisen. How homogene-ous is the area of radon emanation in the Tlamacas area? Is the radon distribution the same at different times? The present article is devoted to a detailed study of the Radon release in the area of Tlamacas; the results were obtained at different times by two different radon survey methods. Similar radon surveys in volcano-tectonic geological structures have been carried out in different active volcanoes all over the world [2]-[6]. The current study aids in understanding the connection of Tlamacas Mountain with the volcano Popocatepetl, which is of great importance for forecasting its eruptive activity.

2. Radon Survey in the Tlamacas Area 2.1. Equipment and Method CR39 solid state nuclear track detectors (SSNTD) were used to determine the detailed distribution of the soil radon concentration in the Tlamacas Mountain in our first survey. Plastic glasses with suspended CR39 detec-tors inside were buried in 40 cm-deep holes in the 30 measurement sites during 15-17-APR-2010 and recovered 09-MAY-2010. The total deployment time of the detectors varied between 22 days 4 hours and 24 days 6 hours.

CR39 was developed by Cartwright [7]. It is a plastic polymer (POLYALLY-DIGLYCOL-CARBONATED or PADC) that belongs to the class of polyesters. This material has the characteristic of being susceptible to al-pha particles resulting from radioactive decay of radon. The impacts of the particles with CR39 create damage on the surface of the detectors; the damage concentration is related to the radon concentration. Damage tracks can be highlighted through a chemical attack carried out using KOH 6.2 M, placed in an oven at a constant tem-perature of 60˚C for 18 hours. During this chemical attack, the detectors are thinned, and the tracks of the dam-ages are enlarged. After this process the tracks can be observed using an optical microscope.

The measurement of track density consists in hand-counting using pictures obtained through a digital camera installed on the microscope. The investigation area covers a surface of 3 mm2 for each detector and counting al-lows us to obtain the number of tracks per square centimeter (tr./cm2). In this work we considered only circular

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Figure 2. Radon concentration in the area of Tlamacas mountain (area marked by ellipse) and between Tlamacas and paso de cortes (top part of the map), 05-DEC-2009.

tracks with a white spot inside, which represent alpha particles that hit the surface of the CR39 detectors per-pendicularly, in order to avoid manufacturing defects.

Absolute values in Bq/m3 are not possible, because we did not use the holders, which prevent radon’s daugh-ter nuclides (e.g. 218Po) from damaging the CR39 sensors. Instead we obtained relative values in tr./cm2, com-parable with others collected in the same conditions and in the same area.

The SARAD RTM 1688 Radon/Thoron monitor was used for our second survey, which was carried out on 05-JUL-2011. Measurement of radon concentration by this instrument is based on the alpha spectrometry me-thod: the concentration of radon is proportional to the number of alpha particles emitted during 222Rn decay in the ionization chamber. The concentration of radon released was measured with 10 min sampling time in 23 sites on Tlamacas Mountain.

Additionally, portable solid state detectors SARAD Scout were used in our preceding study for obtaining ra-don map between Paso de Cortes and Tlamacas and in the Tlamacas Mountain (Figure 1). Details and limitation of this study can be found in [1].

2.2. Results and Discussion Our results (Table 1 and Table 2) are presented in the Figure 3. First, one can see that the spatial distribution of radon release on Tlamacas Mountain is not homogeneous, it has fine structures. Our first measurements with the CR39 detectors reveal 2 active spots of intensive radon emanation with a diameter of about 300 m: one on the northwestern side of the mountain and another on the western side. Our second measurements with the SARAD RTM 1688 monitor show a completely different radon distribution: radon release is observed in three different mountain sides meanwhile the topside is depleted in radon.

What can explain such a considerable difference between 2 periods of measurements? Radon emanation de-pends on a variety of factors, such as deposits of radioactive elements, soil porosity and penetrability, meteoro-logical conditions (almost importantly atmospheric pressure and humidity), the presence of active tectonic structures, and increased fracturing. Naturally, the atmosphere pressure was equal for all measurement sites in so

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Table 1. Concentration of radon obtained with CR39 during April-May 2010.

Lat ˚N Long ˚W Time (days) Tr./cm2

19.061 98.633 24.247 1832

19.062 98.632 24.235 480

19.063 98.631 24.222 420

19.064 98.630 24.211 2042

19.065 98.630 24.199 1141

19.066 98.628 24.186 1502

19.067 98.628 24.170 420

19.068 98.627 24.151 1712

19.068 98.627 24.142 3273

19.067 98.629 24.133 240

19.067 98.628 24.128 6637

19.067 98.625 24.153 571

19.067 98.623 24.139 511

19.068 98.621 24.128 691

19.066 98.621 24.118 1141

19.066 98.623 24.118 1021

19.064 98.626 24.104 180

19.064 98.627 24.104 210

19.066 98.629 23.281 60

19.066 98.630 23.260 571

19.067 98.630 23.247 150

19.068 98.630 23.240 270

19.069 98.629 23.229 961

19.069 98.628 23.219 661

19.069 98.627 22.344 601

19.068 98.625 22.337 811

19.067 98.626 22.330 1351

19.067 98.628 22.215 1832

19.067 98.628 22.198 751

19.066 98.628 22.179 3724

localized an area. A previous study [1] has also excluded the presence of superficial radioactive deposits. How-ever, we cannot rule out the influence of environmental factors together with weather conditions. Our first mea-surements were realized during a long period of fair weather, whereas the second survey was performed during the rainy season. Tlamacas Mountain is inhomogeneously covered by pine trees, and atmospheric precipitation in covered places could make an impact upon soil humidity and even its penetrability. This factor could essen-tially reduce radon release. In addition, the different methodologies of the measurements require care in inter-pretation. Results obtained with the CR39 detectors display the integrated radon contribution during over 3 weeks of measurements whereas the RTM 1688 monitor estimates the current level of radon emanation. Strictly, the reliability factor is higher for CR39 results comparing to the RTM 1688 data.

The above mentioned impact may give up to 30% of deviation in obtained results, but the difference between the two maps is still larger. Instead, the governing factor which may explain the observed phenomenon can be the geological origin of the Tlamacas Mountain. Preliminary, we infer that Tlamacas Mountain resulted from volcanic activity and it likely functions as a parasite crater of volcano Popocatepetl at some time. Hence it may remain an active geological structure, as also confirmed by different phenomena discussed in [1]. In this inter-

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Table 2. Concentration of radon obtained with CR39 during April-May 2010.

Lat ˚N Long ˚W Rn, Bq/m3 Rn err, % 19.0671 98.6281 800 29 19.0670 98.6292 6500 11 19.0674 98.6288 2306 19 19.0674 98.6285 1068 30 19.0674 98.6281 1329 23 19.0674 98.6278 1026 29 19.0673 98.6274 3007 15 19.0671 98.6290 839 29 19.0672 98.6284 1108 30 19.0670 98.6283 355 53 19.0666 98.6283 240 62 19.0666 98.6286 629 33 19.0662 98.6288 530 38 19.0661 98.6292 381 53 19.0664 98.6292 575 38 19.0669 98.6292 602 35 19.0669 98.6296 531 40 19.0665 98.6297 225 68 19.0660 98.6297 140 71 19.0655 98.6294 490 38 19.0656 98.6291 1929 20 19.0658 98.6284 1675 21 19.0669 98.6274 407 55

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Figure 3. Detailed distribution of Radon concentration in Tlamacas Mountain: (a) map obtained with CR39, 15-17-APR- 9-MAY 2010; (b) map obtained with SARAD RTM 1688, 05-JUL-2011. The top of Tlamacas Mountainis approximately in the center of each picture.

pretation, the difference between local radon behavior may be explained by a continued geodynamical processes in the Mountain depths.

3. Conclusions The presented results of two soil radon surveys realized at a different time have confirmed our earlier supposi-tions. Being an active geological structure, Tlamacas Mountain emanates radon in a spatially heterogeneous manner that is non-stationary in time.

It is highly desirable to supplement our current studies by methods of geophysical prospecting and structural geology which may help us to make a scientific leap in understanding the nature of the Mountain and explain better a series of geophysical phenomena observed in its area.

The observed phenomena have substantial significance for our monitoring of geophysical parameters in the Tlamacas Mountain area for the purpose of forecasting eruptive activity of the volcano Popocatepetl.

Acknowledgements This work was partially funded under Mexican UNAM DGAPA PAPIIT projects IN120808 and IN109411. Authors thank G. Espinoza, M. Fazio, P. Perego, F. Foglia, G. Norini and G. Groppelli for their help with mea-suring and processing of CR39 detectors. We are also thankful to J. Berger, X. Carriere, R. Hernández Cardenas and L.J. Cortes Leyva for their participation in measurements with SARAD RTM 1688.

References [1] Kotsarenko, A., Grimalsky, V., Yutsis, V., Pérez, L.I.M., Bravo Osuna, A.G., Koshevaya, S., Perez Enriquez, R., Ur-

quiza Beltran, G., Villegas Ceron, R.A., Lopez Cruz Abeyro, J.A. and Valdes Gonzales, C. (2012) Experimental Stu-dies of Anomalous Radon Activity in the Tlamacas Mountain, Popocatepetl Volcano Area, Mexico: New Tools to

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Study Lithosphere-Atmosphere Coupling for Forecasting Volcanic and Seismic Events. Annals of Geophysics, SI: Earthquake Precursors, 55, 109-118.

[2] Goff, F., Janik, C.J., Delgado, H., Werner, C., Counce, D., Stimac, J.A., Siebe, C., Love, S.P., Williams, S.N., Fischer, T. and Johnson, L. (1998) Geochemical Surveillance of Magmatic Volatiles at Popocatepetl Volcano, Mexico. Gelog-ical Society of America Bulletin, 110, 695-710. http://dx.doi.org/10.1130/0016-7606(1998)110<0695:GSOMVA>2.3.CO;2

[3] Martín, M.C., Ahijado, A., De la Nuez, J., Quesada, M.L., Steinitz, G., Vulkan, U. and Eff-Darwich, A. (2003) Radon Survey at La Palma Island (Canary Islands): First Results. Vulcânica, I, 113-116.

[4] Burton, M., Neri, M. and Condarelli, D. (2004) High Spatial Resolution Radon Measurements Reveal Hidden Active Faults on Mt. Etna. Geophysical Research Letters, 31, L07618. http://dx.doi.org/10.1029/2003GL019181

[5] Hernandez, P., Perez, N., Salazar, J., Reimer, M., Notsu, K. and Wakita, H. (2004) Radon and Helium in Soil Gases at Canadas Caldera, Tenerife, Canary Islands, Spain. Journal of Volcanology and Geothermal Research, 131, 59-76. http://dx.doi.org/10.1016/S0377-0273(03)00316-0

[6] Pulinets, S.A. and Boyarchuk, K.A. (2004) Ionospheric Precursors of Earthquakes. Springer, Berlin, Heidelberg, New York.

[7] Cartwright, B.G., Shirk, E.K. and Price, P.B. (1978) A Nuclear-Track-Recording Polymer of Uniquesensitivity and Resolution. Nuclear Instruments and Methods, 153, 457-460. http://dx.doi.org/10.1016/0029-554X(78)90989-8